On Associations in the Unified Modelling Language

Associations between classifiers are among the most fundamental of UML concepts. However, there is considerable room for disagreement concerning what an association is, semantically. These have implications for the modeller because they can result in serious misunderstandings of static structure diagrams; similarly, they have implications for tool developers. In this paper we describe and classify the variants which have implicitly or explicitly been described. We discuss the scope for, and difficulties in, understanding these as specialisations of a more general notion and we address the implications for future versions of UML.